datetime：舍入/修剪位数，以微秒为单位 [英] datetime: Round/trim number of digits in microseconds

问题描述

目前，我正在记录内容，并且正在使用带有自定义 formatTime（）的我自己的格式化程序：

Currently I am logging stuff and I am using my own formatter with a custom formatTime():

def formatTime(self, _record, _datefmt):
    t = datetime.datetime.now()
    return t.strftime('%Y-%m-%d %H:%M:%S.%f')

我的问题是微秒，％f 是六位数字。无论如何，是否需要吐出更少的数字，例如微秒的前三位？

My issue is that the microseconds, %f, are six digits. Is there anyway to spit out less digits, like the first three digits of the microseconds?

推荐答案

最简单的方法是使用切片仅截去微秒的最后三位数字：

The simplest way would be to use slicing to just chop off the last three digits of the microseconds:

def format_time():
    t = datetime.datetime.now()
    s = t.strftime('%Y-%m-%d %H:%M:%S.%f')
    return s[:-3]

我强烈建议您切碎。我曾经写过一些日志代码，将时间戳四舍五入而不是四舍五入，当四舍五入改变最后一位时，我发现它实际上有点令人困惑。定时代码在某个时间戳记时停止运行，但是由于舍入的缘故，存在带有该时间戳记的日志事件。

I strongly recommend just chopping. I once wrote some logging code that rounded the timestamps rather than chopping, and I found it actually kind of confusing when the rounding changed the last digit. There was timed code that stopped running at a certain timestamp yet there were log events with that timestamp due to the rounding. Simpler and more predictable to just chop.

如果您想真正地舍入数字而不是仅仅进行切碎，则需要更多的工作但并不可怕：

If you want to actually round the number rather than just chopping, it's a little more work but not horrible:

def format_time():
    t = datetime.datetime.now()
    s = t.strftime('%Y-%m-%d %H:%M:%S.%f')
    head = s[:-7] # everything up to the '.'
    tail = s[-7:] # the '.' and the 6 digits after it
    f = float(tail)
    temp = "{:.03f}".format(f)  # for Python 2.x: temp = "%.3f" % f
    new_tail = temp[1:] # temp[0] is always '0'; get rid of it
    return head + new_tail

显然，您可以使用较少的变量来简化上述操作;我只是希望它很容易理解。

Obviously you can simplify the above with fewer variables; I just wanted it to be very easy to follow.

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